Studies of the surface of cell membrane and other physiologically important amphipathic lipids will be carried out primarily using a film balance but when desired will incorporate information from other investigational tools including differential scanning calorimetry, electron spin resonance and nuclear magnetic resonance. Attempts will be made to evaluate the effect of cholesterol in mixed lipid films on the sheer viscosity and water specific evaporative resistance. Pure and mixed monomolecular films involving spin-label and fluorescent probes will also be studied to learn to what extent the probe itself perturbs its own environment, how miscible such probes are in expanded and condensed lipid phases and what possible conformations such probes can adopt and to what extent their relative stability is affected by temperature and lipid composition. Film characterization of acidic phospholipids will continue with particular emphasis on miscibility. A preliminary study of the effects of glycerol and urea also lipid heterogeneity on lipid-protein interactions will be made.